This invention relates to an automotive vehicle with an internal combustion engine having a camshaft with an accumulator.
Automotive vehicle engines with reciprocal pistons typically have a plurality of cylinder combustion chambers with the reciprocating pistons mounted therein. Each piston is pivotally connected with a piston rod, which is pivotally connected with a crankshaft. A timing gear is mounted at an end of the crankshaft. Typically, each cylinder has at least one intake valve and one exhaust valve. Both the intake valve and the exhaust valve are spring-loaded to a closed position. Each intake and exhaust valve is associated with a rocker arm. To operate the valves, the rocker arms are moved by a set of contacting cam lobes. The cam lobes are mounted on an elongated member known as a camshaft. Attached at an extreme end of the camshaft is a camshaft pulley. The camshaft pulley is powered by the crankshaft via a timing chain or belt which is looped over the camshaft pulley and a crankshaft timing gear. Accordingly, the camshaft is synchronized with the crankshaft and the timing of the opening and closing of the intake and exhaust valves is fixed with respect to the position of the piston within the cylinder combustion chamber.
In an effort to improve the environment by decreasing polluting emissions and increasing vehicle gas mileage, it has become desirable to allow the timing of the cylinder valve operation to vary with respect to the piston position within the cylinder chamber. To provide for the variable valve timing operation, a variable camshaft timing unit (VCT) is provided on the camshaft.
An example of a VCT is a dual oil feed vane-type VCT. A dual oil feed vane-type VCT provides an inner member or hub that is fixably connected to an end face of a camshaft. The hub has a series of vanes which are captured in cavities or pressure chambers provided in an outer member which is concentrically mounted on the hub. The outer member incorporates the camshaft timing pulley. The vanes circumferentially bifurcate the pressure chambers into an advance side and a retard side. A spool valve, fluidly communicative with the pressure chambers via the inner member and the camshaft, controls the fluid pressure in the advance side and retard side of the pressure chambers. Accordingly, the angular position of the timing pulley versus the crankshaft can be varied by controlling the fluid in the advance and retard pressure chambers.
Another example of a dual oil feed VCT is a helical gear type VCT. The helical gear type VCT has an outer member attached to an inner member or hub along a helical gear connection. A pressure chamber is provided between the inner and outer members. The pressure chamber is axially bifurcated by a pressure boundary which contacts the outer member to move the same with respect to the inner member. The outer member can axially move with respect to the inner member. The helical gear interconnection between the inner and outer members causes the outer member to rotate with respect to the inner member and accordingly changes angular position with respect to the inner member.
Both of the aforementioned VCTs utilize engine lubricating oil pressure and flow to phase the camshaft. The VCT must meet minimum phase speed requirements to achieve the desired fuel economy and emission benefits as well as acceptable drivability and the avoidance of stumble/stall conditions. Typically, the engine oil pump in most vehicles cannot meet the oil pressure instantaneous flow requirements of a VCT, especially at low engine speeds and high oil temperatures.
To meet the flow volume demand of engine arrangements having multiple VCTs, pressurized oil supply systems with an accumulator or accumulators have been proposed. Accumulators are well-known in the art and typically include a pressure volume enclosed by a shell. Within the shell is a diaphragm or bladder that is depressed by the entry of fluid therein. In the most recent quarter century, to increase the fuel economy of automotive vehicles, most vehicles have had their front end lowered. The lowering of the front end of the vehicle substantially reduces the space available within the engine compartment. Accordingly, it is highly desirable to provide an engine arrangement having an accumulator which does not require additional space within the engine compartment. It is further advantageous to provide an accumulator which does not require the assembly operation of attachment to a vehicle engine. Accumulators have become more desirable due to other features of many automotive engines which require pressurized oil such as hydraulic cam lifters and hydraulically actuated poppet valves.
The present invention brings forth an automotive engine arrangement which includes an engine block having a cylindrical combustion chamber. The combustion chamber mounts a piston for reciprocating movement therein. Passageways are provided through the engine block which connect with the combustion chamber. The passageways have valves for controlling flow through the passageways. The valves are operatively associated with a camshaft that is rotatively mounted in the engine block. The camshaft has an internal cavity for receipt of fluids such as engine lubricating oil. A compliance member is provided within the camshaft cavity for pressurizing the lubricating oil within the camshaft cavity.
The camshaft of the present invention is advantageous in that it provides an accumulator with additional volumetric capacity without requiring additional space within the engine compartment or without any assembly to the automotive engine.
Other advantages of the invention will become more apparent to those skilled in the art upon a reading of the following detailed description and reference of the drawings.